Proportional stroke automatic temperature control system

ABSTRACT

This invention relates to an automatic temperature control system for automobiles and improved components thereof. The control system operates on the proportional stroke principle and comprises an in-car air sensing tube biased with ambient air; a sensor in an aspirator at the end of the tube; a moving pivot operated directly by the output of the sensor; and a feedback control valve operated by the moving pivot for driving a vacuum-assist motor, the output stroke of which operates the various electrical and vacuum functions of the heater-air conditioning system.

This application is a Continuation-In-Part of Ser. No. 422,954, filedDec. 7, 197 , now abandoned.

BACKGROUND OF THE INVENTION

1. Field of the Invention

This invention relates in general to an automatic temperature controlsystem for automobiles, improved components thereof and the arrangementof such components within the system.

2. Description of the Prior Art

Automatic temperature control systems were first introduced in about1964 in the United States and are now available on most large size cars.In the systems heretofore, the components of the system have beenscattered throughout the car, being interconnected by vacuum and wiringharnesses. One of these systems, for instance, has a main componentgrouping on the power servo, with other hardware located on the dashcontrol, in ducts, on the air conditioning case, and in the enginecompartment. Another has many components grouped on the heater-airconditioning case, with other components on the dash control, under thedash and in the engine compartment. These systems are generallycomplicated, difficult to install and maintain, expensive to produce andinaccurate.

The components of such systems and their function are as set forthbelow:

1. Sensors - to sample in-car and ambient temperature;

2. Transducers - to convert the sensors' output to a control signal;

3. A power servo - to convert the control signal to a stroke, therebydriving program switches and a temperature door. Bimetal sensors havebeen used to sense temperature changes and provide a signal responsivethereto for many years. However, the signal from such a sensor is verysmall and is rarely able by itself to provide the necessary force toactivate a mechanical or electrical system of which the sensor is apart;

4. Program switches - to control system functions such as air dischargelocation, blower speed, recirculation, water valve, on-off function,etc.;

5. A temperature blend door - to modulate the air discharge temperaturefrom the heater-air conditioning system;

6. Dash controls - contains levers used by the driver of a car to adjustand set the system to the desired mode and condition of operation;

7. Selector switches - operated by the dash controls;

8. Cold engine lockout (CELO) valve - to delay the system operation inits heater mode until the heater core is warm;

9. Compressor ambient switch - to control the compressor operation as afunction of the ambient temperature;

10. A water valve - controlled by a program switch to turn water off tothe heater core under maximum cooling conditions; and

11. A resistor block - contains a dropping resistor for fan speedcontrol. This works in conjunction with the program switches.

There are many problems associated with these systems. In operation,these systems generally have two sensors which individually sense theambient and in-car temperature and convert these readings to eitherelectronic or mechanical signals. The ambient signal is used to bias thein-car signal and the single output is used to control the operation ofthe system. The appropriate temperature is generally supplied by theoperation of a temperature blend door whose opening and closingregulates the heat and air conditioning supplied from the heater and airconditioner.

Since the sensors are often mounted at the end of long tubes supplyingthe in-car and ambient air, error in the sensing apparatus is oftenintroduced by the air passing through long super-heated stretches whichbias the temperature of the incoming air. For instance, the in-car airis often sampled by letting air enter a tube which is underneath thedash. By the time the air reaches its sensor near the fire wall, thetemperature of the air in the tube has often reached an elevatedtemperature compared to that of the original air by reason of biasoccurring when the air passed through heated areas under the dash. Thisproblem has sometimes been corrected by placing both sensors at the spotwhere sampling air was taken in, but this requires long electrical leadsand electrical conversion signals for changing the temperature of theair sensed to an appropriate electrical value.

In these systems, the output stroke of the power servo is proportionalto the vacuum level therein which in turn is proportional to the sensorsignals from the two sampling devices. This is called a "proportionalvacuum" system. A proportional vacuum system is subject to strokehysteresis, i.e., there may be two different output strokes at the samevacuum level. As the transducer signal does not have a feedback loop,the sensors and transducers combination does not know where the servomotor stroke is at any given time, which causes drift, cycling andover-shoot.

Hysteresis is caused by the frictional forces required to drive theprogram switches, to open the temperature doors, by the overridesprings, and by various pin hole tolerances. Further, hysteresis is notconstant from one system to another and will deteriorate with time.

In these prior art systems, as the vacuum level increases, the servomotor strokes towards maximum air conditioning mode operation while withdecreasing vacuum the servo motor drives towards maximum heaterconditon. The friction in the system, however, causes the stroke toreach different positions for the same temperature, depending on whetherthe vacuum is increasing or decreasing. Current systems take two stepsto alleviate these conditons and effect acceptable control. One is toprovide high vacuum levels so that the slope of the control curveincreases. This serves to decrease the differences in stroke for thesame temperature. The second means used is to provide low frictionprogram switches. These two means do serve to reduce hysteresis, butthey present problems themselves in that the use of high vacuum level ishard to attain on the present-day automobiles with their numerouspollution control devices, especially on long hill climbs and the use oflow friction switches is expensive.

There are two types of vacuum motors, or power servos, currently used tosupply output to a shaft from a supply of vacuum. These are often usedto operate car doors, as well as to drive switches in an automatictemperature control system. Generally, these motors consist of two casehalves (the cylinder) which entrap a diaphragm upon which is mounted arigid piston with an output shaft. One case half has a port connected toa source of vacuum and the other half is open. As vacuum is variedthrough the port, the motor strokes towards and away from the case halfcontaining the port.

One type of such motor in use now is called a rolling diaphragm motor.Here as the piston strokes towards the case half containing the portwhen vacuum is increased, the diaphragm transfers from the piston areato the cylinder. This provides maximum effective area for the cylinderdiameter and allows the motor to take large pressure differences.However, the piston must always support the diaphragm requiring verydeep case halves and the pressure differential cannot be reversed.

A second type of such motor or servo in present use is the flip-flopdiaphragm motor. Here the diaphragm does not transfer from the piston tothe case and had no defined convolute. This motor has the advantage ofhaving a shallower case than does the rolling diaphragm motor and themotor can take pressure reversal. However, it requires a larger diameterfor the same effective area achieved in a rolling diaphragm motor and itcannot take as much pressure differential as the rolling diaphragm motorcan.

Vacuum switches or valves are used in automotive applications in anon-off mode to apply vacuum to various places within the system to openand shut air supply doors, etc. In the automatic temperature controlsystem of the present invention, vacuum switches are used for suchthings as determining the air discharge location, blower speed,recirculation operation mode, water valve operation, etc. Several typesof such switches are presently on the market, all of which have certaindisadvantages.

One type is generally made of two die case pieces which are lappedsmooth. Ports are provided in one half while the other has channels sothat when the second half is rotated it either provides a channel fromone port to the other so that vacuum can be switched from one port toanother, or it closes the ports. These switches have generally requireda fairly high force to overcome friction and cross-venting of the portshas resulted in serious vacuum leakage and loss of vacuum, especially onlong hill climbs. This loss of vacuum causes a loss of control in all ofthe vacuum systems.

Another such switch has the movable portion made of rubber, which ismolded to a metal plate. Here the switch has very small ports, on theorder of 0.020 inches, with relatively large rubber sealing contactareas. The small size of the ports often allows blockage due to frost oraccumulation of dirt.

A type of valve used to produce porportional vacuum is what is known asa dog bone valve. This has three modes of operation as follows:

1. At rest, the dog bone component seals off both the vacuum and ventports so that there is no operation of the overall valve;

2. A diaphragm in the dog bone valve allows a vent body which surroundsthe dog bone components to move in response to outside forces. When thevalve is to supply additional vacuum, the valve body pulls upon the dogbone component and releases it from its seat, thereby allowing thevacuum level of the valve to increase to the supply level unless the dogbone component is first returned to its rest position; and

3. When vacuum is to be decreased, the vent body is moved further intothe valve until it is released from contact with the dog bone component,thus allowing venting of the vacuum within the valve. This ventingcontinues until the vent body returns to its rest position in contactwith the dog bone component.

SUMMARY OF THE INVENTION

This invention is for an improved automatic temperature control systemfor automobiles whereby the operator may set a desired in-cartemperature and the control system will operate the heater and airconditioning systems to keep the in-car temperature at the selectedmark.

It provides an accurate means of maintaining the selected temperature byeliminating frictional losses and providing for low hysteresis, inreducing the amount of vacuum450000000000000000000000000000000000000000000000000000000000000000

